Oil-replacement additive for reducing emissions from two-stroke engines

ABSTRACT

An oil-replacement additive for two-stroke engine fuel capable of reducing fuel consumption, enhancing combustion and reducing emissions comprises boron and a carrier, wherein the boron concentration in said additive is in the interval of 100 to 600 ppm, the carrier comprises an alcohol, the amount of oil in the additive is less than 10% (w/w), and the balance is a fuel. Most preferably said additive is substantially oil-free. A two-stroke fuel comprising said additive, and a significantly reduced amount of oil, or substantially no oil, said fuel having a boron concentration in the interval of about 1 to 12 ppm.

TECHNICAL FIELD

The present disclosure relates generally to fuel additives for improving the function and reducing the emissions from two-stroke engines as well as fuel mixtures containing such additives. The disclosure relates in particular to oil-replacement additives.

BACKGROUND

A two-stroke engine is a type of internal combustion engine which completes a power cycle with only two strokes (up and down movements) of the piston during one crankshaft revolution. In comparison, a “four-stroke engine”, requires four strokes of the piston to complete a power cycle. In a two-stroke engine, the end of the combustion stroke and the beginning of the compression stroke happen simultaneously, with the intake and exhaust functions occurring at the same time.

Two-stroke engines have been in commercial use for over a century, and remain very popular still today as they usually have a high power-to-weight ratio, a greatly reduced number of moving parts, can be more compact and therefore also significantly lighter than four-stroke engines.

Spark ignition versions of two-stroke engines, i.e. two-stroke engines using gasoline or similar volatile fuel, are particularly useful in lightweight applications such as motorcycles, three-wheelers, snowmobiles, outboard motors, and the like, and preferably in handheld high-power applications such as chain saws, trimmers etc. In these and similar applications, the two-stroke engine has offered an affordable and flexible source of power. In developing countries, two-stroke engines have become extremely popular in small vehicles such as motorcycles, scooters, three-wheelers, tuk-tuks and the like, providing affordable and flexible means of transport.

In four-stroke engines, lubrication is achieved by oil held in an oil sump. The oil is distributed through the engine by splash lubrication or a pressurized lubrication system, including an oil pump. Unlike a four-stroke engine, which is a more advanced construction, two-stroke engines use a total-loss lubrication system where fuel and oil are combined to provide both energy and lubrication. In an oil-injected two-stroke engine, the oil is injected directly into the engine, where it mixes with the fuel. Many two-stroke engines however require a pre-mixed fuel-oil mixture.

Crankcase-compression two-stroke engines, such as the common small gasoline-powered two-stroke engines, create more exhaust emissions than four-stroke engines because lubricating oil is mixed with the fuel, and burned in the engine. The tell-tale blue smoke is typical for two-stroke engines. The lack of strict emission regulations in many parts of the world and the high number of motorized light vehicles results in high emissions. In many cities two-stroke engines are among the main sources of urban air pollution.

The main pollutants in exhaust fumes from two-stroke engines, of course depending on several factors, such as the fuel used, are particulate matter (PM), total hydrocarbons (THC), volatile organic compounds (VOCs), and nitrogen oxides (NOx). Carbon dioxide (CO₂) and carbon monoxide (CO) formed in the combustion of organic fuels are also noteworthy emissions, as they contribute to the greenhouse effect and climate change.

There are many health and environmental issues related to air pollution from combustion engines. High levels of air pollution are linked to respiratory problems, for example allergies, asthma, and acute respiratory infections. Emissions of particulate matter are linked to an increased risk for cardiovascular diseases. Needless to say, CO₂ contributes to the greenhouse effect and climate change.

In U.S. Pat. Ser. No. 6,783,561, Ali Erdemir presents a method for providing enhanced lubricity in fuels and lubricants wherein a boron compound is added to said fuel or lubricant. Erdemir is focused on reducing or eliminating sulfur in the fuel, and has investigated the anti-wear properties of low-sulfur fuel with different additions of boron. Erdemir suggests boron concentrations from about 30 ppm to about 3000 ppm, about 200 to about 2000 ppm, alternatively from about 50 to about 1000 ppm, or from about 100 ppm to about 500 ppm.

An international patent application, WO 2005/083042, presents an additive for two-stroke engines where the amount of oil is reduced and a lubricating effect is achieved by an addition of boron. It is suggested that 10-90% of the oil is replaced by fuel or a hydrocarbon carrier, for example an alcohol. However, according to a preferred embodiment, only 10-60% of the oil is replaced, and the boron content of the additive is in the range 1500-2500 ppm. The application contains no examples.

Problems with the stability of boron solutions i.e. a tendency of aggregation and sedimentation, has however hampered the large scale use of boron containing additives.

Later, Tommy Lindblom and Magnus Undén developed a method for producing stable boric solutions, disclosed in international patent application WO 2010/134872 and patented for example in U.S. Pat. No. 9,222,045. The method addresses the difficulties in producing a stable boric solution, i.e. avoiding aggregation and precipitation during storage. The method results in a boron solution with desired particle size, and which is stable over time. According to their findings, the finished fuel, after adding the additive produced by their method, should reach a boron concentration within the range 10-10 000 ppm, preferably within the range 20-30 ppm. A higher concentration, up to 10 000 ppm pertains primarily to use in more solid lubricants.

The Safety Data Sheet concerning an early product, the “Triboron Fuelenhancer”, issued 25, Feb. 2008 and revised 1, Feb. 2012 concerns an additive for regular 4-stroke fuels. According to the Safety Data Sheet, the additive contained ethanol, butanone, isobutyl methyl ketone and ethyl acetate in addition to boric acid.

SUMMARY

The present inventors have surprisingly found that two-stroke engines can be operated with a significantly reduced amount of oil, and in a preferred embodiment, in the total absence of oil.

A first aspect of the invention is an oil-replacement additive for two-stroke engine fuel, said additive comprising boron and a carrier, wherein the boron concentration in said additive is in the interval of 1 to 600 ppm, the carrier comprises an alcohol, the amount of oil in the additive is less than 10% per weight, and the balance is a fuel.

According to a preferred embodiment of said first aspect, the amount of oil in the additive is less than 8%, preferably less than 6%, more preferably less than 4%, and most preferably less than 2% per weight.

More preferably said additive the amount of oil in the additive is less than 1% per weight, and most preferably the additive is substantially oil-free.

According to another embodiment, freely combinable with the above aspects, said alcohol is chosen from methanol, ethanol, propanol, and butanol, and said balance of fuel is a fuel having a flash point similar to that of the two-stroke fuel to which the additive is intended to be added.

According to a preferred embodiment, again freely combinable with the above aspects, the concentration of boron is in the interval of about 10 to about 600 ppm, preferably about 100 to about 600 ppm. More preferably, the concentration of boron is in the interval of about 100 to about 300 ppm.

According to another embodiment, freely combinable with the above aspects, the boron is added in the form of a stable boron solution prepared by dissolving a boron compound in an alcohol, followed by vigorous mixing and exclusion of particles larger than 100 nm.

A second aspect is a novel two-stroke engine fuel comprising an additive according to the above aspect and embodiments thereof, wherein the boron concentration in the fuel is in the interval of 1 to 12 ppm. Preferably the boron concentration is in the interval of 1 to 6 ppm., most preferably about 2-3 ppm.

According to an embodiment of the second aspect, the fuel contains less than 1% oil (w/w).

A third aspect relates to a method for reducing the emissions from a two-stroke engine, wherein an additive comprising boron dissolved in an alcohol, less than 10% oil (w/w), the balance being a fuel and the concentration of boron in said additive is the interval of 1 to 600 ppm, preferably in the interval of 10 to 600 ppm, most preferably about 100 to 300 ppm is added to the fuel.

According to an embodiment of said third aspect, said additive is mixed into the fuel at a proportion of about 1 part additive to 100 parts fuel.

According to another embodiment, said additive is injected into the cylinder together with fuel at a proportion or about 1 part additive to 50 parts fuel.

Importantly, the invention allows the enhancement of combustion in two-stroke engines, a significant reduction of the emissions of total hydrocarbons (THC), CO and CO₂ with maintained or even improved lubrication of the two-stroke engine.

DESCRIPTION OF EMBODIMENTS

Before the present invention is described, it is to be understood that the terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims and equivalents thereof.

It must be noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

Where the concentration of boron is indicated in ppm, this refers to the concentration of elemental boron in mg/kg corresponding to ppm.

The term “oil” is used to indicate any oil, natural or synthetic, currently used in two-stroke engines. Two-stroke oils are sometimes referred to as two-cycle oils, 2-cycle oils, 2T oil or “petroil”. A characteristic requirement is that two-stroke oils must have a lower ash content compared to regular lubricating oils, as the two-stroke oil is burned along with the fuel. The base oil is either petroleum, castor oil, semi-synthetic or synthetic oil or various mixtures thereof. Currently, synthetic oils are more frequently used, and different types of two-stroke oils have been developed for specialized uses and engine types. The fuel to oil mixing ratio ranges from 16:1 to as low as 100:1. The emission problems are of course most accentuated at high mixing ratios, but they remain also at lower ratios. In modern two-stroke engines, the mixing ratio is generally low, 1-2%.

Lubricating oils are traditionally added to two-stroke fuel either by mixing in the fuel when filling up the tank, by using pre-mixed fuel, or by direct injection from a separate oil tank. For many hand-held two-stroke engine powered tools, and in particular for older or simpler engines, mixing the lubricating additive into the fuel when refueling appears to be the most usual method. In more advanced two-stroke engines, a separate oil tank is provided, and the lubricating additive is automatically injected when the engine is in operation. The additive disclosed herein is applicable to all of these methods. It is conceived that the oil-replacing additive is mixed into the bulk of fuel at a ratio of approximately 1 part additive to 100 parts fuel (approximately 1 or continuously added or injected, at a ratio of approximately 1 part additive to 50 parts fuel (approximately 2%).

The general understanding until now has been that an addition of a low concentration of boron is effective to reduce friction and wear in four-stroke engines. This has been successfully tested in field tests using passenger cars, i.e. advanced four-stroke engines. A significant, or complete elimination of oil in two-stroke engine fuel has however—to the best knowledge of the present inventors—not been disclosed.

The present inventors have investigated how the concentration of boron influences the emissions, the rate of combustion, and fuel consumption in two-stroke engines.

In their experimental work using different two-stroke engines, the inventors surprisingly found that the amount of oil could be significantly reduced, and even substantially eliminated, with maintained lubrication and with improved combustion, reduced fuel consumption and reduced emissions. More surprisingly still, this effect was achieved at significantly lower boron concentrations than previously believed to be possible.

A first aspect of the invention is an oil-replacement additive for two-stroke engine fuel, said additive comprising boron and a carrier, wherein the boron concentration in said additive is in the interval of 1 to 600 ppm, the carrier comprises an alcohol, the amount of oil in the additive is less than 10% (w/w), and the balance is a fuel.

Different sources of boron can be used. It is for example possible to use a boron compound such as a crystalline boric acid, boron oxide, boron trioxide etc. It is however preferable to use an oxygen-bearing boron compound such as boric acid (H₃BO₃) of pharmaceutical quality, i.e. with a purity of preferably at least 99% and a molecular weight of 61.8 g/mol. An alternative is to use boron oxide (B₂O₃), with a molecular weight of 69.6 g/mol, also known as anhydrous boric acid, also of pharmaceutical quality. A stable boric solution where no particles are larger than 100 nm is then prepared for example according to the methods set out in WO2010134872, incorporated herein by reference.

According to a preferred embodiment of said first aspect, the amount of oil in the additive is less than 8%, preferably less than 6%, more preferably less than 4%, and most preferably less than 2% per weight.

More preferably said additive the amount of oil in the additive is less than 1% per weight, and most preferably the additive is substantially oil-free.

According to another embodiment, freely combinable with the above aspects, said alcohol is chosen from methanol, ethanol, propanol and butanol, and said balance of fuel is a fuel having a flash point similar to that of the two-stroke fuel to which the additive is intended to be added. Preferably said fuel is the same as the fuel to which the additive is intended to be added. In standard two-stroke applications, this is frequently standard 95 octane unleaded gasoline.

The flash point of a fuel is the lowest temperature where enough fuel can evaporate to form a combustible concentration of gas. In spark-ignition engines, fuel is mixed with air and ignited by the spark plug. There are standardized test methods for the measurement of flash points, well known to persons skilled in the art.

The above embodiment where the fuel or carrier in the additive has a flash point similar to that of the fuel to which it is intended to be added, has a particular advantage. When the oil-replacement additive comprises a fuel with the same flash point as the bulk of fuel to which it is added, both fuels will combust simultaneously, and the additive will increase the effect of the engine. In contrast, when traditional two-stroke oils and oil containing additives are used, the oil obviously has a higher flash point, and will not contribute to the combustion, or does so only to a limited degree. As a matter of fact, using traditional two-stroke fuels and oils, a large portion of the oil is not at all, or only partially combusted, which adds to the exhaust fumes and increases pollution.

According to a preferred embodiment, again freely combinable with the above aspects, the concentration of boron is in the interval of 10 to 600 ppm, preferably about 100 to 600 ppm. More preferably, the concentration of boron is in the interval of 100 to 300 ppm.

According to another embodiment, freely combinable with the above aspects, the boron is added in the form of a stable boron solution prepared by dissolving a boron compound in an alcohol, followed by vigorous mixing and exclusion of particles larger than 100 nm.

Methods for the production of a stable boron solution are disclosed in WO 2010/134872, incorporated by reference in its entirety. This method involves vigorous mixing and a settling step. The boron is incorporated in an organic solvent or a fuel, preferably first incorporated in an alcohol and then diluted to the desired concentration using a hydrocarbon carrier and/or a fuel. Preferably said fuel is the same fuel as the fuel to which the additive is intended to be added, or a fuel compatible with this fuel. In two-stroke applications, the fuel is preferably unleaded 95 octane gasoline. Kerosene and naphtha can also be used as carriers and/or diluents in the additive.

Without wishing to be bound by any theory, the inventors contemplate that the stable boron solution produced according to the methods disclosed in WO 2010/134872 is one key factor behind the surprising results. It is contemplated that the controlled particle size <100 nm and/or the electrostatic charge of the particles contribute to the superior lubricating properties, making it possible to eliminate the use of oil already using a very low concentration of boron.

Consequently, a second aspect is a novel two-stroke engine fuel comprising an additive according to the above aspect and embodiments thereof, wherein the boron concentration in the fuel is in the interval of 1 to 12 ppm. Preferably the boron concentration is in the interval of 1 to 6 ppm, most preferably 2-3 ppm.

According to an embodiment of the second aspect, the fuel contains less than 1% oil (w/w). The bulk of said fuel is preferably standard two-stroke fuel, such as but not limited to unleaded 95 octane gasoline.

A third aspect relates to a method for reducing the emissions from a two-stroke engine, wherein an additive comprising boron dissolved in an alcohol, less than 10% oil (w/w), the balance being a fuel and the concentration of boron in said additive is the interval of 1 to 600 ppm, preferably in the interval of 100 to 600 ppm, is added to the fuel.

According to an embodiment of said third aspect, said additive is mixed into the fuel at a proportion of about 1 part additive to 100 parts fuel. This is usually called a “premix” but has so far only referred to oil-containing mixtures. Premix ratios vary with the requirements of different engines, and a skilled person can figure out a suitable ratio starting from the above guidance, e.g. about 1 part additive to 100 parts fuel.

According to another embodiment, said additive is injected into the cylinder together with fuel at a proportion or about 1 part additive to 50 parts fuel. Many two-stroke engines are equipped with separate oil tanks and an oil injection system, and the presently claimed additive can advantageously be applied also to such systems, e.g. prefilled in the oil tank and then injected into the cylinder during operation of the engine. Again, a skilled person can adjust the settings of the injection system starting from the above guidance, e.g. about 1 part additive to 50 parts fuel.

One advantage with the inventive additives, fuels and methods is that the emissions are significantly reduced, in particular the emission of total hydrocarbons and carbon monoxide. At the same time, the combustion efficiency is increased, and the fuel consumption was reduced. It is clear that a combination of reduced emissions and reduced fuel consumption is a significant advantage. The examples show that the invention allows the reduction of the emissions of total hydrocarbons, CO and CO₂ with maintained lubrication of the two-stroke engine.

The combined effects are also very surprising. Additionally, the first experiments were performed without intermediate cleaning of the engine, and it appears that the effects of the boric acid additive remains for a while. This lingering effect is likely attributable to the controlled particle size and/or the electrostatic charge of the particles.

An additional advantage is that boron, unlike many other compounds that have been used or are suggested for use in lubricating additives, is non-toxic and has no known impact on the environment. As a matter of fact, boron is generally considered to be non-toxic at levels normally encountered, and boron is widely used cosmetics, products for oral hygiene, bath products and products for waving hair. In these applications, the allowed concentration (expressed as boric acid) ranges from 0.1 to 18%, which is significantly higher than the ppm concentrations disclosed herein.

According to the “Opinion on Boron Compounds issued in 2010 by the Scientific Committee on Consumer Safety (SCCS/1249/09), boric acid is considered non-mutagenic based on the available in vitro data. No data regarding a possible association between cancer and boron exposure in humans has been found. In fact, different boron compounds and in particular boric acid is already widely used in cosmetics and healthcare products. Boron compounds are also widely used in agriculture, as a component of fertilizers.

EXAMPLES Example 1 A Comparative Example

The present inventors commissioned a study to be performed at an accredited research institute (SMP, Svensk Maskinprovning AB, part of RISE). The performance of a modern, commercially available chain saw was studied in a test bench, investigating the possibility to reduce or eliminate the addition of oil to the two-stroke fuel.

Materials

Engine oil: Commercial engine oil for two-stroke engines was used (Stihl standard oil “Low smoke 2 Stroke oil”).

Oil replacement additive: An oil replacement additive was prepared by mixing a stable ethanol solution of boric acid, prepared according to the methods of WO 2010/134872 with an amount of the above engine oil. In the final additive, the amount of oil was 30% and the balance a mixture of kerosene and ethanol.

Fuel: Standard, commercial two-stroke fuel (unleaded 95 octane gasoline) was used. Standard oil was added to the fuel according to the engine manufacturer's instructions, i.e. 2 parts oil to 98 parts fuel (volume). In this test, the oil replacement additive was however added in a smaller amount, 1 part additive to 99 parts fuel (volume).

Two-stroke engine: A modern, commercially available chain saw (Stihl, Model MS181) was used. This chain saw has a 31.8 cc engine with a nominal effect of 1.5 kW.

Methods

The method used for differentiate the two-stroke mixtures, a standard oil and an additive according to embodiments of the present disclosure, was the G3 Standard Cycle (according to ISO standard 8178-4:2007), performed using a chain saw as defined above. The ISO 8178 is an international standard for exhaust emission measurement from a number of non-road engine applications. It is used for emission certification and/or type approval testing in many countries, including the United States, European Union and Japan. Depending on the legislation, the cycle can be defined by reference to the ISO 8178 standard, or else by specifying a test cycle equivalent to ISO 8178 in the national legislation (as it is the case with the US EPA regulations).

The ISO 8178 includes a collection of steady-state engine dynamometer test cycles (designated as type C1, C2, D1, etc.) designed for different classes of engines and equipment. Each of these cycles represents a sequence of several steady-state modes with different weighting factors.

The emissions, i.e. selected pollutants in the exhaust, were measured according to the methods disclosed in ISO 8178 and EC Directive 97/68.

Tests using the standard oil were designated A and A2, and tests using a boric acid containing additive according to the invention were designated B and B4. The test procedure was as follows:

-   1. A shorter warm-up run (15 min) using (A) with 2% injection,     followed by -   2. The actual test run with a load of 100% and 0% respectively, and     simultaneous collection of data (fuel consumption, temperature,     emission). -   3. A shorter warm-up run (15 min) using (B) with 1% injection,     followed by -   4. The actual test run with a load of 100% and 0% respectively, and     simultaneous collection of data (fuel consumption, temperature,     emission). -   5. A shorter warm-up run (15 min) using (A2) with 2% injection,     followed by -   6. The actual test run with a load of 100% and 0% respectively, and     simultaneous collection of data (fuel consumption, temperature,     emission). -   7. A shorter warm-up run (15 min) using (B4) with 1% injection,     followed by -   8. The actual test run with a load of 100% and 0% respectively, and     simultaneous collection of data (fuel consumption, temperature,     emission).

It should be noted that this chain saw (Stihl MS181) has an automatic carburetor (IntelliCarb™ Compensating Carburetor) designed to automatically adjust the air/fuel ratio when the air filter becomes restricted or partially clogged and it thus maintains the engine's correct RPM. Therefore there was no tuning of the carburetor between test runs. It is contemplated that by tuning the carburetor, the reduction in fuel consumption and emissions would have become even more pronounced.

The fuel consumption and the specific fuel consumption are shown in Table 1 below. It is evident that replacing the standard two-stroke oil with a boric acid containing additive according to an embodiment significantly reduces fuel consumption and enhances combustion. Enhanced combustion is here evidenced as increased cylinder head temperatures.

TABLE 1 Fuel consumption and combustion efficiency A. HP Super A2. Syntetic B. Standard B4. C. Standard Additive oil Additive Additive oil 2% 1%. 2% 1% No oil Engine 1.2 1.3 1.4 1.2 1.3 performance [kW] [±2%] RPM 10000 9981 10018 9981 10004 Specific fuel 536 480 444 501 452 consumption [g/kWh] [±3%] Change: −10% −17% −7% −16% Fuel 625 613 594 584 577 consumption at rated speed [g/h] [±2%] Change:  −2%  −5% −7%  −8% Cylinder 260 265 270 268 283 head temperature [° C.] [±2%]

In tests A and A2, a high performance super synthetic standard oil was added to the fuel to a concentration of 2%. In B and B4, the inventive additive was used together with 1% oil in the fuel, and in C, the additive was used without any addition of oil.

As there was no cleaning of the engine between the test runs B and A2, a remaining effect of the boric acid can be seen. Further tests investigating this phenomenon will be performed.

Without wishing to be bound by any theory, the inventors contemplate that there is a lasting effect of the boric acid, due to interactions between the boric acid and inner surfaces of the engine. Earlier research shows the existence of a thin film, confirmed by scanning electron microscope (SEM) investigations.

The results show that the boron containing additive significantly reduced both the specific fuel consumption and the fuel consumption at rated speed. The increase in cylinder head temperature indicates a more effective combustion. The reduction in fuel consumption and the increased temperature was most significant in test C, where the inventive additive was used alone, without any addition of oil.

In five test runs, the exhaust gases were collected and analyzed. The average values are presented in Table 2.

TABLE 2 Specific emissions (g/kWh) Specific emission (g/kWh) A2. A. B. Standard B4. C. Standard oil Additive oil Additive Additive 2% 1% 2% 1% No oil THC + Nox 47.9 41.63 42.11 44.43 39.83 −13% −12% −7% −17% THC [±8%] 45.4 38.56 37.46 40.44 36.96 −15.07%   −17.49%   −10.93%    −18.59%   CO [±8%] 264.32 203.66 152.41 194.36 212.37 −23% −42% −26%  −20% CO2 [±8%] 1156 1095 1060 1170 996  −5%  −8%  1% −14% NOx [±8%] 2.5 3.07 4.65 3.99 2.87  23%  86% 60% 15%

Tests A and A2, B and B4, and C represent the same conditions as above. The results show a significant reduction in exhaust emissions, seen for total hydrocarbons (THC), CO and CO₂ as evident from Table 2. The increase in NOx is however an expected result from the enhanced combustion and increased temperature. This can possibly be addressed by fine-tuning the carburetor.

Further tests are necessary to obtain repeatable results, but the results so far already show that an unexpected and highly desirable reduction of the amount of oil that is added to two-stroke engine fuel can be achieved through the use of a boric acid containing additive.

Example 2 Boron Additive Reduces Wear Scar Formation

Friction reduction and wear scar formation was investigated for different two-stroke fuel mixtures, using a high-frequency reciprocating rig according to ISO standard 12156. The boron concentration was determined for each sample, Finally, a coefficient of friction (CoF) was determined for each sample. See Table 3.

TABLE 3 Wear scar and CoF Test 1 Elemental analysis (oil) Test 2 Boron conc. HFRR Wear Information mg/kg Scar Sample (FF5.5 w %, red ASTM EN ISO Sample ID Naphta 50%) D51185 mod 12156 CoF 1 003-39 2T Inj (B mg/kg 210 225 0.100 212) 2 003-40 2T Inj (B mg/kg 390 182 0.104 415) 3 003-41 2T Inj (B mg/kg 130 201 0.104 128)

As can be seen in Table 3, the calculated boron concentration was confirmed by the elemental analysis. All concentrations were in the interval of 100 to 600 ppm (128 (130) ppm; 212 (210) ppm; and 415 (390) ppm). Further, the determination of wear scar and coefficient of friction confirmed the usefulness of the additive.

Example 3 On-Going Multi-Variable Studies

The present inventors have commissioned a further study, based on the ISO-standard, but with the following modifications:

-   -   the test engine will be operated for a longer duration when         changing from an additive according to embodiments of the         invention to a standard oil, in order to see how long the effect         of the boric acid can be seen, or     -   the test engine will be cleaned between test runs, in order to         avoid “carry over” of previous test conditions     -   different concentrations of boric acid will be tested, for         example 200 mg/kg boron resulting in 2 and 4 mg/kg boron in the         fuel depending on whether the boron containing oil-replacement         additive is injected into the engine, or pre-mixed into the fuel     -   different concentrations of oil in the additive will be tested,         ranging from 0% to 30% per weight.

In another set-up, also commissioned by the present inventors, different compositions will be tested. The boron concentration in the additive will be in the interval of 1 to 100 ppm, resulting in a concentration of 0.01 to 1 in the fuel.

Similarly, the amount of oil will be in the interval of 0 to 30% of the additive, resulting in a concentration of 0 to 0.3 or 0.6% oil in the fuel after final mixing or injection. Compared to standard two-stroke oils and two-stroke fuels, this represents a significant reduction all the way to a total removal of the oil component.

Preliminary results indicate that already a very low boron concentration makes it possible to reduce the amount of oil. A boron concentration in the interval of 0.01 to 1 ppm in combination with a minimal addition of oil significantly reduces the emissions and improves fuel combustion and as a consequence, reduces fuel consumption.

Using a higher concentration of boric acid, but one which still is very low compared to previously disclosed concentrations, for example a concentration in the interval of 0.1 to 1 ppm, no oil needs to be added to the two-stroke fuel.

Without further elaboration, it is believed that a person skilled in the art can, using the present description, including the examples, utilize the present invention to its fullest extent. Also, although the invention has been described herein with regard to its preferred embodiments, which constitute the best mode presently known to the inventors, it should be understood that various changes and modifications as would be obvious to one having the ordinary skill in this art may be made without departing from the scope of the invention which is set forth in the claims appended hereto.

Thus, while various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. 

1. An oil-replacement additive for two-stroke engine fuel, said additive comprising boron and a carrier, wherein the boron concentration in said additive is in the interval of 1 to 600 ppm, the carrier comprises an alcohol, the amount of oil in the additive is less than 10% (w/w), and the balance is a fuel.
 2. The additive according to claim 1, wherein the amount of oil in the additive is less than 8% (w/w).
 3. The additive according to claim 1, wherein the amount of oil in the additive is less than 1% (w/w).
 4. The additive according to claim 1, wherein said alcohol is chosen from methanol, ethanol, propanol, and butanol, and said balance of fuel is a fuel having a flash point similar to that of the two-stroke fuel to which the additive is intended to be added.
 5. The additive according to claim 1, wherein the concentration of boron is in the interval of 10 to 600 ppm.
 6. The additive according to claim 1, wherein the concentration of boron is in the interval of 100 to 300 ppm.
 7. The additive according to claim 1, wherein the boron is added in the form of a stable boron solution prepared by dissolving a boron compound in an alcohol, followed by vigorous mixing and exclusion of particles larger than 100 nm.
 8. A two-stroke engine fuel comprising an additive according to claim 1, wherein the boron concentration in the fuel is in the interval of 1 to 12 ppm.
 9. The two-stroke engine fuel according to claim 8, wherein the boron concentration is in the interval of 1 to 6 ppm.
 10. The two-stroke engine fuel according to claim 8, wherein the boron concentration is about 2 to 3 ppm.
 11. The two-stroke engine fuel according to claim 8, wherein the fuel contains less than 1% oil (w/w).
 12. A method for reducing the emissions from a two-stroke engine, wherein an additive comprising boron dissolved in an alcohol, less than 10% oil (w/w), the balance being a fuel and the concentration of boron in said additive is the interval of 1 to 600 ppm, is added to the fuel.
 13. The method according to claim 12, wherein said additive is mixed into the fuel at a proportion of about 1 part additive to 100 parts fuel.
 14. The method according to claim 12, wherein said additive is injected into the cylinder together with fuel at a proportion or about 1 parts additive to 50 parts fuel.
 15. The method according to claim 12, wherein the additive is added in an amount resulting in reduced emissions of total hydrocarbons, CO and CO₂ with maintained lubrication of the engine.
 16. The additive according to claim 1, wherein the amount of oil in the additive is less than 6%(w/w).
 17. The additive according to claim 1, wherein the amount of oil in the additive is less than 2%(w/w).
 18. The additive according to claim 1, wherein the additive is substantially oil-free.
 19. The additive according to claim 1, wherein the concentration of boron is in the interval of 100 to 600 ppm.
 20. The method of claim 12, wherein said additive is the interval of 100 to 600 ppm. 